Name and define the five distinct ideas in Darwin’s theory of evolution by natural selection.

Question

I need two more theses are the ones I have:
Populations show variation for almost all traits.
Certain variations improve survivorship and the number of offspring left (improve fitness) If these variations are heritable, their frequency increases each generation.

Are theses even right?

Since this is not my area of expertise, I searched Google under the key words "Darwin 'natural selection'" to get these possible sources:

http://anthro.palomar.edu/evolve/evolve_2.htm
http://en.wikipedia.org/wiki/Natural_selection
http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html
(Broken Link Removed)
http://www.talkorigins.org/faqs/darwinism.html

I hope this helps. Thanks for asking.